Cold cathode indicator tube



June 1965 G. A. KUPSKY ETAL 3,183,511

COLD GATHODE INDICATOR TUBE Original Filed Nov. 10. 1960 INVENTOR. ROGER WOLFE y GEORGE fl./|UP$K) 0/? W0 GLASER RT TORNEY United States Patent This'invention relates to cold cathode gaseous indicator tubes.

This is a continuationof application Serial No. 68,450, filed November 10, 1960 now abandoned.

One type of cold cathode gaseous indicator tube presently available includes a plurality of cathode electrodes which are adapted to exhibit cathode glow; that is, a sheath of gas surrounding a cathode glows under proper electrical excitation. In this type of .tube, the cathodes are mounted on a pair of support posts and are insulated fromeach other by means of cylindrical insulating spacers which are threadedon the support posts. It has been found that, at times during the preparation or operation of a tube of this type, particles of cathode metal are sputtered from the cathode surfaces and are. deposited on allportions ofthe tube including the insulating spacers. Under some circumstances, so much of this sputtered material deposits on the spacers that conductive shorting paths form between adjacent electrodes which should be insulated from each other. This condition prevents normal operation of the tube.

The purposes and objects of the present invention concern the provision of an improved multiple cathode indicator gas tube in which the adverse effects of cathode sputtering are minimized, and the shorting of adjacent electrodes due to sputtering are substantially overcome.

Briefly, a cold cathode indicator tube embodying the invention includes a stack of cathode electrodes mounted on a plurality of support posts with insulating spacers between them. According to the invention, the portions of the cathode electrodes which are mounted on the support posts and the insulating spacers between the cathodes are shaped so that the effective. path length of the insulatingelements is a maximum while the straight-line spacing betweencathodes is a minimum. in addition, in one embodiment of the invention, the insulating spacers are shaped so that a portion of the adjacent cathode electrode is prevented from glowing. With this construction, continuous leakage paths of sputtered cathode material are prevented from forming on the insulating elements between cathodes.

The inventionis described in detail by reference to the single sheet of drawings wherein:

FIG. 1 is a perspective view, partly in section, of a coldcathode gaseous indicator tube embodying the invention;

FIG; 6 is a sectional side elevational view of a por tionof a tube embodying another modification of the in- V vention; and

FIG. 7 is a sectional side elevational view of a portion of a tube embodying still another modification of the invention.

. 3,188,511 Patented June 8, 1%65 Referring to FIGS. 1, 2, and 3, a cold cathode gaseous indicator glow tube 10, according to the invention, includes an envelope 12 which has been evacuated and filled with a gas such' as neon or the like at a suitable pressure to sustain cathode'glow. The pressure may be in the range of about 30 to about mm. of Hg. The envelope includes a base, or stem 14, through which metal pins 16 extend and by means of which electrical connection is made to suitable external electrical circuit' elements. Two diametrically opposed pins 16' are longer than the others and are adapted to receive and support the various electrodes of the tube and, accordingly, are provided with a suitable insulating coating (not shown). The envelope 12 also includes a transparent viewing'window 20 through which glowing indicator cathode electrodes 22 are viewed. A sealed off exhaust tubulation (not shown) is provided in the stem 14.

The indicator cathode electrodes 22 of the tube 10 may take substantially any desired shape; for example, they may benumbers, letters, or the like, and any convenient' number of cathodes may be'provided. The cathode elements 22" are made of any suitable'metal, for example, stainless steel, aluminum, nichrome, molybdenum, or the like, and they may be made in any suitable fashion, for example, by etching, stamping, or the like.

The indicator cathodes 22 have opposed, generally planar upperand lower surfaces 24 and 26,-.respectively, and each cathode is provided with oppositely disposed apertured mounting tabs28 and 30, by means of which the cathodes are mounted and supported on posts 16. Each tab is, in efiiect, a continuation of its cathode and includes opposed, substantially planar upper and lower surfaces 32and 34 which are coextensivewith. the cathode surfaces 24 and 26. Each cathodeis also provided with at least one electrical lead 36" extending from one of its tabs 28 or 30' to a pin 16. The cathode elements 22 are stacked on the posts 15'- one above the other, parallel to each other, and facing the viewing window 29 of the envelope l2;

The cathode elements 22 are mounted on the posts 16' with insulatingspacers 38, of glass, ceramic, or the like, threaded onthe posts 16; between them. The spacers 38 are generally cylindrical and include planar upper and lower surfaces 39 and 40'. The spacers rest on the cathode tabs and, preferably, have alarger. area than the tabs so that they substantially cover the tabs. A conductive mesh screen electrode 41' is mounted at the top of the cathode stack, and the entire stack of electrodes is locked on the posts' 16 by mica rings or eyelets 42 or by any suitable means provided at the tops of the posts 16'. The screen electrode 41 comprises either the entire anode or part of the anode assembly for the tube 19 and'is provided with suitable electrical connection to a pin 16.

The tube 10 also includes a cup-shaped electrode 44' which receives and encloses the stack of electrodes supported on the posts 16. The cup has a base 45' and a side wall 4-8. A pair of diametrically opposed longitudinal slots 50 and 52 are provided in the wall of the cup adjacent to and aligned with the support posts 16'.. The cathode leads 36 extend through the slots 50 and 52, preferably with adjacent leads extending through opposite slots. The cup 44 may be operated as part of the tube anode assembly, if desired, and, if so used,"it is electrically connected to the screen 41 and/or to one of" the pins 16 in any suitable manner. The cup 4 4 may be connected to the screen 41 by means'of a metal tab 43" or the like.

According to the invention, in'order'to prevent shorting between adjacent cathodes 22'due to the deposition. of

sputtered cathode metal on the insulating spacers 38 the cathode electrodes in the vicinity of their attachment to the snsaerr mounting posts 16' are shaped to increase the total length of the insulating path between them. This increase in path length is achieved without an increase in the straightline spacing between adjacent cathodes. Referring to FIGS. 3 and 4, a portion of each of the apertured tabs 28 and 30 is removed to form notches or depressions which provide each tab with a region 53 and 55, respectively, of reduced thickness. The regions 53 and 55 originate at about the boundary between each tab and the indicator cathode 22 associated therewith and extend almost to the center of the aperture in each tab. The inner portion of each insulating spacer which faces toward a cathode 22 lies over one of the regions 53 or 55, and it can be readily seen that the length of the potential shorting path between adjacent cathodes is thus increased to an optimum length for the intended purpose. The straight-line spacing between the surface 53' of the portion 53 and the surface 55' of the portion 55, and the facing surface of the adjacent insulating spacer 38 must be small enough, that is, less than the length of the cathode dark space, so that the portions 53 and 55 do not exhibit cathode glow when the indicator character portion 22 adjacent thereto glows. Those skilled in the art understand that this spacing varies with gas pressure. At a gas pressure of about mm. of Hg, the spacing may be about four or five mils. This spacing is understood to be maintained in all of the embodiments of the invention described below.

In another modification of the invention shown in FIG. 5, the path length between adjacent cathodes is increased still further by utilizing specially shaped insulating spacers 54 instead of the cylindrical spacers 38 shown in FIG. 2. Thus, in FIG. 5, the ceramic spacers 54 have convex surfaces 56 and 58, instead of planar surfaces as in FIG. 3.

In the modification of the invention shown in FIG. 6, the cathodes 22 and the cathode tabs 28 and 30 are of uniform thickness and the portions 53 and of reduced thickness are not provided. In order to achieve the desired insulating path length between adjacent cathodes, this modification of the invention includes insulating spacers 60 which are generally cylindrical and include upper and lower surfaces 62 and 64. A raised central ring-like portion 66 is provided on one or both surfaces of each spacer surrounding posts 16' to provide the desired length of surface between adjacent cathodes. The portions 66 are of smaller diameter than the spacers 60. Of course, if desired, the cathode tabs may also be notched as in FIGS. 3 and 4.

A similar modification of the invention shown in FIG. 7 includes insulating spacers 68 which are cylindrical in form and have plane parallel opposed surfaces 70 and 72. Cathodes 74 are provided having opposed apertured tabs 76 including opposed surfaces 78 and 80. In this embodiment of the invention, the tabs 76 are provided with annular raised portions 82 surrounding the posts 16' extending therethrough. The portions 82 are of smaller diameter than the tabs 76. Thus, in this modification of the invention, the raised portion is provided, not on the spacer, but on the cathode tab itself. The raised portion 82 may be integral with the cathode tab 76 and may be made at the same time that the cathode is made, or it may be a separate element. The raised portions may also be provided on one or both-surfaces 78 and 80 of each cathode tab 76.

In the forms of the invention shown in FIGS. 6 and 7,

'it may also be desirable to limit the height of the raised portions 66 (FIG. 6) and the raised portions 82 (FIG. 7) so that the portions of the cathode tab and insulating spacer which'face each other are also parallel to each other and are spaced apart by a distance smaller than the cathode dark space. Thus, these portions of the cathode electrodes will not glow, and there will be no sputtered material on the facing surfaces of the insulating spacers.

Under some circumstances, particularly in the forms of the invention shown in FIGS. 3 and 5, it may be desirable to provide a barrier to prevent the deposition of sputtered metal onto portions of the insulating spacers remote from the portions of reduced thickness of the cathodes. To this end, referring to FIGS. 1 and 2, the cup electrode 44 is provided with shield members which are adapted to shield the aforementioned portions of the insulating spacers from cathode material which might be sputtered thereon. Preferably, four shields are provided, one for each edge of the slots. The shields are generally L-shaped and include one wall 92 which is secured to the inner surface of the cup and another wall 94 which lies against the column of spacers and thus effectively shields them from the cathode numbers; The shields extend along substantially the entire length of the column of spacers on the posts 16'. The shields may be formed as integral portions of the cup wall, or they may be separate members welded or otherwise secured thereto.

The invention described herein provides a multi-cathode indicator tube in which a compact stack of closelyspaced cathodes may be employed with substantially no problem of shorts developing between cathodes due to sputtered cathode metal. The features of construction which are embodied in the invention are favorably simple and economical.

What is claimed is:

1. A cold cathode gaseous indicator tube comprising an envelope having a gas filling suitable for sustaining cathode glow, an anode electrode, a plurality of glow cathode electrodes which sputter and emit metal particles in operation, 7

each cathode having a pair of apertured mounting tabs which are mechanically and electrically connected thereto, the pairs of mounting tabs being aligned on two parallel axes,

support posts threaded through and engaging said mounting tabs and supporting said cathodes parallel to each other in a stack in said envelope,

and generally annular insulating spacer bodies threaded on said posts between adjacent cathodes for providing insulation therebetween,

each spacer being in contact with a cathode mounting tab on either side of it,

each spacer also including a projecting portion which projects from the support post on which the spacer is mounted into the space between adjacent cathode electrodes and is spaced from the adjacent cathodes whereby the length of the surface of a spacer body from its region of contact with the cathode mounting tab on one side to its region of contact with the oathode mounting tab on its other side is greater than I the perpendicular distance between adjacent cathodes,

at least a portion of the surface of said projecting portion being positioned parallel to and close to the surface of the adjacent cathode which it faces.

2. The tube defined in claim 1 wherein said cathode tabs have opposed planar surfaces with at least one sur face including a depression in the region of contact between the tab and an associated one of said insulating spacer bodies, said depression lying adjacent to but spaced from the surface of the associated spacer body and thus increasing the path length extending from one cathode and along the surface of a spacer body to the next adjacent cathode.

3. The tube defined in claim 1 wherein said cathode tabs have opposed planar surfaces with at least one surface including a depression in the region of contact between the tab and an associated one of said insulating spacer bodies, and each insulating spacer body includes opposed surfaces at least one of which is generally convex whereby the combination of the convex surface and the depression in the cathode tab provide a path length, from one cathode along a spacer body to the next adjacent cathode, which is greater than the perpendicular distance between adjacent cathodes.

4. The tube defined in claim 1 wherein each insulating spacer body is in the form of a toroid and has opposed planar surfaces and each cathode tab has opposed planar surfaces, at least one surface of each cathode tab also including an annular step member which spaces the adjacent cathode electrode therefrom and provides a path length, from one cathode along a spacer surface to the next cathode, which is greater than the perpendicular distance between adjacent cathodes.

5. The tube defined in claim 1 wherein each insulating spacer body is in the form of a toroid and has opposed planar surfaces and each cathode tab has opposed planar surfaces, at least one surface of each cathode tab also including an annular step member of smaller diameter than the cathode tab itself, the step member serving to space adjacent cathode electrodes apart and provide a path length, from one cathode along a spacer surface to the next cathode, which is greater than the perpendicular distance between adjacent cathodes.

6. The tube defined in claim 1 wherein each insulating spacer body is in the form of a toroid and has opposed planar surfaces and each cathode tab has opposed planar surfaces, at least one surface of each insulating toroid also including an annular step member which increases the spacing between adjacent cathode electrodes and provides a path length, from one cathode along a spacer surface to the next cathode, which is greater than the perpendicular distance between adjacent cathodes.

7. A cold cathode gaseous indicator tube comprising an envelope having a gas filling suitable for sustaining cathode glow,

an anode electrode,

a plurality of glow cathode electrodes,

each cathode having a pair of mounting tabs disposed at substantially dimetrically opposed portions thereof, corresponding mounting tabs of said pairs being aligned on a common axis,

a lead coupled to one tab of each cathode,

a generally cup-shaped member enclosing said cathode electrodes and including a pair of opposed slots,

support posts engaging said mounting tabs and supporting said cathodes in a stack in said envelope with each cathode having one of its tabs aligned with one of said slots in said cup-shaped member so that each cathode lead extends through one of the slots,

insulating spacers disposed between adjacent cathodes for providing insulation therebetween, each spacer being in contact with a cathode on either side of it, each spacer having an irregularly curved surface, including a portion parallel to and close to the adjacent cathode tab, so that the length of the surface of a spacer from its region of contact with a cathode on one side to its region of contact with the cathode on its other side is greater than the perpendicular distance between adjacent cathodes, and

shield means secured to said cup-shaped member in the vicinity of the slots therein and shielding said insulating means from the cathodes lying inside said cup.

References Cited by the Examiner UNITED STATES PATENTS 1,171,598 2/l6 Defukest 313-268 X 1,537,903 5/25 Von Lepel 313268 X 2,878,407 3/59 Engleman et a1 313-109.5

2,906,906 9/59 McCauley et al 313-2l0 X 2,916,649 12/59 Levin 313-268 X FOREIGN PATENTS 1,048,347 1/59 Germany.

GEORGE N. WESTBY, Primary Examiner. 

1. A COLD CATHODE GASEOUS INDICATOR TUBE COMPRISING AN ENVELOPE HAVING A GAS FILLING SUITABLE FOR SUSTAINING CATHODE GLOW, AN ANODE ELECTRODE, A PLURALITY OF GLOW CATHODE ELECTRODES WHICH SPUTTER AND EMIT METAL PARTICLES IN OPERATION, EACH CATHODE HAVING A PAIR OF APERTURED MOUNTING TABS WHICH ARE MECHANICALLY AND ELECTRICALLY CONNECTED THERETO, THE PAIRS OF MOUNTING TABS BEING ALIGNED ON TWO PARALLEL AXES, SUPPORT POSTS THREADED THROUGH AND ENGAGING SAID MOUNTING TABS AND SUPPORTING SAID CATHODES PARALLEL TO EACH OTHER IN A STACK IN SAID ENVELOPE, AND GENERALLY ANNULAR INSULATING SPACER BODIES THREADED ON SAID POSTS BETWEEN ADJACENT CATHODES FOR PROVIDING INSULATION THEREBETWEEN, EACH SPACER BEING IN CONTACT WITH A CATHODE MOUNTING TAB ON EITHER SIDE OF IT, EACH SPACER ALSO INCLUDING A PROJECTING PORTION WHICH PROJECTS FROM THE SUPPORT POST ON WHICH THE SPACER IS MOUNTED INTO THE SPACE BETWEEN ADJACENT CATHODE ELECTRODES AND IS SPACED FROM THE ADJACENT CATHODES WHEREBY THE LENGTH OF THE SURFACE OF A SPACER BODY FROM ITS REGION OF CONTACT WITH THE CATHODE MOUNTING TAB ON ONE SIDE TO ITS REGION OF CONTACT WITH THE CATHODE MOUNTING TAB ON ITS OTHER SIDE IS GREATER THAN THE PERPENDICULAR DISTANCE BETWEEN ADJACENT CATHODES, AT LEAST A PORTION OF THE SURFACE OF SAID PROJECTING PORTION BEING POSITIONED PARALLEL TO AND CLOSE TO THE SURFACE OF THE ADJACENT CATHODE WHICH IS FACES. 